>>12465436690%+ of the cast were worthless in DBZ as well. The thing when something is less combat-focused is that someone can be relevant without being a powerful fighter. It's why Nami or Usopp are relevant in One Piece.
Bulma was somewhat relevant in DB because of her various capsule things, as well as her being the cause of searching out the DBs in the first place. Goku would be happy to just wander around the forest and kicking pterodactyls in the dick for the rest of his life.
Once you get to the point where it's "My ki is better than yours, rargh!" then it's hard for anyone to matter a damn if they're not on Goku or Gotenks level. I mean, back to One Piece, at this very moment most of the characters are unusually NOT that relevant because it's now just a pissing contest between Doflamingo and Luffy.